下列符号哪一个代表质谱中最重要的参数？（）
A、M+1峰
B、质核比（m/z）
C、M+2峰
D、M峰
E、相对强度RI
参考答案：B
But Obama’s appearance presented a deeper challenge, reflecting the tenor of his times. Unlike those tragedies---which, at least initially, united a mournful country and quieted partisan divisions---this one has, in the days since the killings, had the opposite effect, inflaming the divide.
盾构是用来开挖土砂类围岩的隧道机械，其组成部分不包括( )。
A．附属装配式构件B．切口环C．盾尾D．支撑环
